Throughout this application, various publications are referenced. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications are hereby incorporated by reference into this application to describe more fully the art to which this invention pertains.
Progression through the cell cycle is marked by a series of irreversible transitions that separate discrete tasks necessary for faithful cell duplication. These transitions are negatively regulated by signals that constrain the cell cycle until specific conditions are fulfilled. Entry into mitosis, for example, is inhibited by incompletely replicated DNA or DNA damage (Weinert and Hartwell, 1988). Another feedback pathway delays the transition from M to G1 if the mitotic spindle is defective (Hoyt et al., 1991; Li and Murray, 1991). These restrictions on cell cycle progression are essential for preserving the fidelity of the genetic information during cell division (Hartwell and Weinert, 1989). The transition from G1 to S phase, on the other hand, coordinates cell proliferation with environmental cues, after which the checks on cell cycle progression tend to be cell autonomous (Hartwell et al., 1974; Pardee 1974, 1989). Among the extracellular influences that restrict cell cycle progression during G1 are proteins that inhibit cell proliferation, growth factor or amino acid depletion, and cell-cell contact. Disruption of these signaling pathways uncouples cellular responses from environmental controls and may lead to unrestrained cell proliferation.
Transitions between phases of the cell cycle are catalyzed by a family of cyclin-dependent kinases (Cdks) (Nurse, 1990; Hartwell, 1991). In some organisms the physiological signals controlling the G2 to M transition target a series of steps that activate the mitotic Cdk, Cdc2. Cdc2 activation is positively regulated by phosphorylation on threonine-161 (Booher and Beach, 1986; Krek and Nigg, 1991; Gould et al., 1991; Solomon et al., 1990; 1992) and negatively by phosphorylation on tyrosine-15 (Gould and Nurse, 1989). Incomplete DNA replication delays dephosphorylation of tyr-15 (Dasso and Newport, 1990; Smythe and Newport, 1992), and mutations in Cdc2 that convert tyr-15 to a nonphosphorylatable residue are lethal and cause a premature mitosis (Gould and Nurse, 1989). Similarly, either over expression of the tyr-15 phosphatase, Cdc25 (Enoch and Nurse, 1990; Kumagai and Dunphy, 1991), or loss of the tyr-15 kinases (Ludgren et al., 1991) bypass the requirement that DNA replication be completed before mitosis begins. Additional levels of control are probably required to fully explain the block to mitosis caused by ongoing DNA replication (Sorger and Murray, 1992; Heald et al., 1993; Stueland et al., 1993). There is also evidence that cell cycle arrest induced by DNA damage may be related to inactivation of Cdc2 (Rowley et al., 1992; Walworth et al., 1993), but the role of tyrosine phosphorylation in this context has been questioned (Barbet and Carr, 1993).
There is some evidence, particularly in yeast, that signals inhibiting the G1 to S phase transition block Cdk activation. The mating pheromone alpha factor arrests the S. cerevisiae cell cycle in G1 (Reid and Hartwell, 1977), and this correlates with a decrease in CDC28 kinase activity and a decline in the abundance of active complexes containing G1 cyclins and CDC28 (Wittenberg et al., 1990). The FARl protein binds to G1 cyclin-CDC28 complexes in cells treated with alpha factor, and this is probably necessary for cell cycle arrest (Chang and Herskowitz, 1990; Peter et al., 1993). Other inhibitors of CDC28 kinase activity have been identified, but their relationship to physiological signals that control cell cycle progression is not known (Mendenhall, 1993; Dunphy and Newport, 1989).
Mammalian cells, like yeast, require cyclin-dependent kinases for progression through G1 and entry into S phase (D""Urso et al., 1990; Blow and Nurse, 1990; Furukawa et al., 1990; Fang and Newport, 1991; Pagano et al., 1993; Tsai et al., 1993). Both D and E-type cyclins are rate limiting for the G1 to S transition and both reduce, but do not eliminate, the cell""s requirement for mitogenic growth factors (Ohtsubo and Roberts, 1993; Quelle et al., 1993). There is little information, however, concerning the manner by which these cyclins and Cdks are negatively regulated by extracellular signals that inhibit cell proliferation.
It has been studied how two signals that block the cell cycle in G1, cell-cell contact and TGF-xcex2, affect the activity of a G1 cyclin-dependent kinase, Cdk2 (Paris et al., 1990; Elledge and Spotswood, 1991; Koff et al., 1991; Tsai et al., 1991; Elledge et al., 1992; Rosenblatt et al., 1992). The cell cycle of Mv1Lu mink epithelial cells can be arrested in G1 by growth to high density. These contact inhibited cells express both cyclin E and Cdk2, but cyclin E-associated kinase activity is not present (Koff et al., 1993). Entry into S phase can also be prevented if Mv1Lu cells are released from contact inhibition in the presence of TGF-xcex2, and this correlates with a block to phosphoryla-tion of the Retinoblastoma (Rb) protein (Laiho et al. 1990). Both Cdk2 and Cdk4 have been implicated as Rb kinases (Matsushime et al., 1992; Hinds et al., 1993; Kato et al., 1993; Ewen et al., 1993a; Dowdy et al., 1993), suggesting that TGF-xcex2 induced cell cycle arrest may involve inhibition of Cdks during G1 (Howe et al., 1991). Consistent with this, cells arrested in late G1 by TGF-xcex2, like contact inhibited cells, express both cyclin E and Cdk2 but do not contain catalytically active cyclin E-Cdk2 complexes (Koff et al., 1993). Cdk4 synthesis is also repressed by TGF-xcex2 (Ewen et al., 1993b). The inactivity of Cdk2 together with the absence of Cdk4 may explain the block to Rb phosphorylation in these cells.
It is shown herein that contact inhibited and TGF-xcex2 treated cells, but not proliferating cells, contain a titratable excess of a 27 kD protein that binds to the cyclin E-Cdk2 complex and prevents its activation. The inhibitory activity of p27 can be competed by the cyclin D2-Cdk4 complex, suggesting that p27 and cyclin D2-Cdk4 may function within a pathway that transmits growth inhibitory signals to Cdk2.
The subject invention provides an isolated 27 kD protein capable of binding to and inhibiting the activation of a cyclin E-Cdk2 complex. The subject invention further provides related recombinant nucleic acid molecules, host vector systems and methods for making same. Finally, the subject invention provides methods of identifying agents and using agents which act on or mimic p27 function, so as to exploit the regulatory role of p27 in cell proliferation.
The subject invention provides an isolated protein having an apparent molecular weight of about 27 kD as measured by SDS polyacrylamide gel electrophoresis, and capable of binding to and inhibiting the activation of a cyclin E-Cdk2 complex.
The subject invention further provides a recombinant nucleic acid molecule which encodes the protein of the subject invention.
The subject invention further provides a vector comprising the recombinant nucleic acid molecule of the subject invention.
The subject invention further provides a host vector system for the production of a protein having an apparent molecular weight of about 27 kD as measured by SDS polyacrylamide gel electrophoresis, and capable of binding to and inhibiting the activation of a cyclin E-Cdk2 complex, which comprises the vector of the subject invention in a suitable host.
The subject invention further provides a method for producing a protein having an apparent molecular weight of about 27 kD as measured by SDS polyacrylamide gel electrophoresis, and capable of binding to and inhibiting the activation of a cyclin E-Cdk2 complex, which comprises growing the host vector system of the subject invention under conditions permitting the production of the protein and recovering the protein produced thereby.
The subject invention further provides a method of determining whether an agent is capable of specifically inhibiting the ability of p27 protein to inhibit the activation of cyclin E-Cdk2 complex which comprises: (a) contacting suitable amounts of p27 protein, cyclin E, Cdk2 and the agent under suitable conditions; (b) subjecting the p27, cyclin E, Cdk2, and agent so contacted to conditions which would permit the formation of active cyclin E-Cdk2 complex in the absence of p27 protein; (c) quantitatively determining the amount of active cyclin E-Cdk2 complex so formed; and (d) comparing the amount of active cyclin E-Cdk2 complex so formed with the amount of active cyclin E-Cdk2 complex formed in the absence of the agent, a greater amount of active cyclin E-Cdk2 complex formed in the presence of the agent than in the absence of the agent indicating that the agent is capable of specifically inhibiting the ability of p27 protein to inhibit the activation of cyclin E-Cdk2 complex.
The subject invention further provides a method of determining whether an agent is capable of specifically enhancing the ability of p27 protein to inhibit the activation of cyclin E-Cdk2 complex which comprises: (a) contacting suitable amounts of p27 protein, cyclin E, Cdk2 and the agent under suitable conditions; (b) subjecting the p27, cyclin E, Cdk2, and agent so contacted to conditions which. would permit the formation of active cyclin E-Cdk2 complex in the absence of p27 protein; (c) quantitatively determining the amount of active cyclin E-Cdk2 complex so formed; and (d) comparing the amount of active cyclin E-Cdk2 complex so formed with the amount of active cyclin E-Cdk2 complex formed in the absence of the agent, a lesser amount of active cyclin E-Cdk2 complex formed in the presence of the agent than in the absence of the agent indicating that the agent is capable of specifically enhancing the ability of p27 protein to inhibit the activation of cyclin E-Cdk2 complex.
The subject invention further provides a method of treating a subject having a hyperproliferative disorder which comprises administering to the subject a therapeutically effective amount of an agent capable of specifically enhancing the ability of p27 protein to inhibit the activation of cyclin E-Cdk2 complex in the hyperproliferative cells of the subject, so as to thereby treat the subject.
The subject invention further provides a method of treating a subject having a hypoproliferative disorder which comprises administering to the subject a therapeutically effective amount of an agent capable of specifically inhibiting the ability of p27 protein to inhibit the activation of cyclin E-Cdk2 complex in the hypoproliferative cells of the subject, so as to thereby treat the subject.
The subject invention further provides a method of diagnosing a hyperproliferative disorder in a subject which disorder is associated with the presence of a p27 protein mutation in the cells of the subject, which comprises determining the presence of a p27 protein mutation in the cells of the subject, said mutation being associated with a hyperproliferative disorder, so as to thereby diagnose a hyperproliferative disorder in the subject.
The subject invention further provides a pharmaceutical composition which comprises an effective amount of a recombinant virus capable of infecting a suitable host cell, said recombinant virus comprising the nucleic acid molecule of the subject invention, and a pharmaceutically acceptable carrier.
Finally, this invention provides a method for treating a subject suffering from a hyperproliferative disorder associated with the presence of a p27 protein mutation in the cells of the subject, which comprises administering to the subject an amount of the pharmaceutical composition of the subject invention effective to treat the subject.